1. Field of the Invention
The present invention relates, generally, to a method and system for configuring a radio interface and, more specifically, to a method and system for configuring a radio interface between a mobile station and a base station in a time-division multiplex mobile radio system for a packet data transmission.
2. Description of the Prior Art
Connection-oriented concepts and concepts based on logic links may be used to transmit data between two communications terminals. In the case of connection-oriented data transmissions, physical resources must be provided between the two communications terminals throughout the entire time of data transmission.
Permanent provision of physical resources is unnecessary for data transmission via logical links. One example of such data transmission is packet data transmission. In this case, a logic link exists between the two communications terminals throughout the entire duration of data transmission, but physical resources are provided only during the actual transmission times for the data packets. This method is based on the fact that the data is transmitted in short data packets, between which relatively long pauses may occur. In the pauses between the data packets, the physical resources are available for other logic links. A logic link results in a saving of physical resources.
The packet data transmission method known from German Patent Specification DE 44 02 930 A1 can be used, in particular, for communications systems with limited physical resources. For example, in mobile radio systems such as the GSM mobile radio system (Global System for Mobile Communications), the physical resources in the frequency band number of frequency channels and time slotxe2x80x94are limited and must be used economically.
The GSM mobile radio system is one example of a time-division multiplex mobile radio system in which time slots within a frequency channel can be split between different communications terminals. The radio station at the network end of a mobile radio network is a base station which communicates with mobile stations via a radio interface. Transmission from a mobile station to the base station is called the uplink direction and transmission from the base station to a mobile station is called the downlink direction. A channel, which is reserved for packet data transmission, is formed by at least one time slot per time-division multiplex frame. Furthermore, the channel is defined by the carrier frequency and any frequency jump sequence.
The GSM mobile radio system was originally conceived for voice transmission, and one channel was reserved for continuous information transmission between the mobile station and the base station. However, for packet data transmission, a common channel is used for packet data transmission for a plurality of mobile stations. In addition to the packet data, signalling information is also transmitted, for which a time slot is provided at cyclic intervals within the channel.
The distinction between logic links and physical connections also means that, although a logic link exists for a mobile station, no packet data is transmitted over a certain time interval. However, as long as there is no transmission from the mobile station to the base station, it is impossible for the base station to carry out any measurements relating to the transmission conditions from the mobile station. Previously calculated values lose their validity and must be redefined during renewed allocation of physical channels, or the base station must ensure that the transmission conditions are set in such a manner that reliable transmission is possible in every case. The latter leads, for example, to an excessive, or even maximum, transmission power setting.
As a result, the present invention is directed to a method and a system for configuring a radio interface for packet data transmission, in which the time delay for passing through a configured radio interface between a mobile station and a base station is reduced.
According to the present invention, time slots for signalling for the uplink direction are allocated to the mobile stations in accordance with a sequence which can be predetermined. The allocation is independent of packet data transmission from or to the mobile station. As a result of this fixed allocation of a time slot for signalling even to mobile stations to which no physical channel is currently allocated, the base station can carry out continuous measurements with regard to the radio interface. When packet data transmission resumes, immediately valid measurements are therefore available for configuration of the radio interface.
Furthermore, a plurality of time slots for signalling within the channel for packet data transmission can be combined to form a signalling block for configuration of the radio interface. In this case, the time slots need not belong to immediately successive frames. Such a signalling block is particularly important for the downlink direction, since information for configuration of the radio interface for the mobile station, for example the transmission level and the timing advance, are contained in it. The combination of time slots to form a signalling block results in the time duration to completion of the signalling block at the receiving end being minimal. The mobile stations are, as a result, quickly supplied with the information required for configuration of the radio interface. Signalling to the plurality of mobile stations is possible via one signalling block. The combination of the configuration data in a message saves transmission capacity which is now available for adjacent cell measurements or other signalling information.
According to an embodiment of the present invention, a plurality of successive time slots for packet data transmission in the channel are also combined to form a packet data block. Since information from a plurality of time slots first forms a packet data block, it is possible to interleave the information in a packet data block and to simplify reconstruction of the information. The interleaving also can be applied to the signalling data.
The configuration data for a mobile station can, in this case, be transmitted together with the configuration data for other mobile stations in a single time slot for signalling. In the downlink direction, in this case, it is advantageously repeated or provided with a coding or error detection, or in a plurality of non-successive time slots for signalling it is transmitted. In the latter case, the interleaving provides error protection. It is possible to set the time slots which are combined to form such a signalling block. In the case of such use, for example, of every other time slot for signalling, the time slots in between can be used for adjacent cell measurements.
The proportion of time slots for adjacent cell measurements can be further increased if less configuration data is transmitted (for example, only the timing advance) or only a small number of mobile stations need to be supplied. In this case, cyclic adaptation of the combination sequence may be provided. Such adaptation improves the matching of the signalling complexity to the actual requirements of the mobile stations for packet data transmissions.
According to the present invention, a closed control loop for the timing advance can be achieved since time slots for signalling are allocated to mobile stations in the uplink direction, and signalling blocks for the mobile stations arrive, with a short time delay, in the downlink direction. Advantageously, only the mobile station and the base station are involved in this control loop. Since, in contrast to packet data transmission, no specific arrangement is required between a mobile station and a data block for this signalling (this is normally carried out in a base station controller), the base station can set the timing advance on its own. In this case, there is no signalling complexity between the base station and the base station controller.
The configuration of the timing advance and the transmission power setting are carried out independently of one another, according to another embodiment of the present invention. The timing advance is defined by a closed control loop between the mobile station and the base station, it being possible to provide a longer cycle between two definitions by suitable selection of the time slots for signalling. Since the motion of the mobile station is relatively slow in comparison with the signal propagation speed, the timing advance need be defined only at intervals of several seconds.
In the process of defining the transmission power setting for the base station, the transmission power is advantageously matched to the mobile station having the poorest transmission conditions on the common channel. To this end, open or closed control loops can be set up independently of the definition of the timing advance. If there are major differences between the transmission powers required for the individual mobile stations and if a plurality of common channels are available, it is advantageous to allocate the mobile stations to the channels on the basis of the transmission power required.
Packet data transmission is advantageously carried out in both transmission directions; that is, in both the uplink direction and the downlink direction, independently of one another. As such, a mobile station can transmit data in the uplink direction or can receive data from the network in the downlink direction. Packet data transmission in both directions also can be provided for a mobile station. The separation into the uplink and downlink directions allows great flexibility in the use of the radio resources and, of course, in the design of the mobile stations, which possibly only transmit or receive.
According to another embodiment, in addition to the designations within the mobile radio system for packet data transmission, the mobile stations are designated by abbreviated identifiers. One or more time slots for signalling in the uplink direction are allocated, via the time slots for signalling in the downlink direction, to the mobile stations by means of indicator messages containing abbreviated identifiers and time slot designations. The abbreviated identifiers allow improved resource utilization between the network and the mobile stations via the radio interface since they are independent of addresses that are known in the network for the mobile stations.
A self-contained message is advantageously transmitted to the base station from a mobile station within a time slot for signalling. This self-contained message contains, for example, received values from the mobile station for signals from the base station. This makes it possible for the base station transmission power to be set immediately for packet data transmission in the downlink direction. Since one closed message is transmitted per time slot, this reduces the time required before the mobile station reception level is available at the base station as well as the time for configuration of the radio interface. The base station uses transmissions for signalling in the uplink direction to define the timing advance and the reception level at the base stations with regard to the respective mobile station. The signalling, which takes place independently of the packet data transmissions, also can be used to request radio resources. The mobile station can thus, request, for example, wanted data channels in the uplink direction without any special call by the base station. This likewise reduces the delay times before packet data transmission.
The value and control value, or values and control values, defined for the timing advance and the transmission power are transmitted to the mobile station in the downlink direction. This also allows it to make the necessary settings for configuration of the radio interface.
The configuration process is further sped up if the definition of the timing advance and/or of the reception level of the base station is also carried out from the time slots for packet data transmission. The setting time for the configuration process also can be influenced by the allocation of abbreviated identifiers to mobile stations. If, for example, a plurality of abbreviated identifiers are allocated to one mobile station, the setting time is shortened. It is likewise possible to keep the delay times short by appropriate choice of specific abbreviated identifiers at the end of a macroframe. Limiting the number of abbreviated identifiers also leads to a capability to reuse a time slot for signalling for a mobile station more quickly and to a shortening of the delay time. The number of abbreviated identifiers is advantageously set to correspond to the transmission conditions and to the number of mobile stations provided for the packet data service.
If a plurality of time slots for signalling in the downlink direction are combined to form a signalling block, then the signalling advantageously takes place simultaneously for a plurality of mobile stations. However, the signalling in the downlink direction can likewise take place within packet data so that, for example, the transmission power setting can be adapted continuously without using time slots for signalling, wherein additional time slots are available for adjacent cell measurement.
The choice of specific transmission block types also allows the signalling complexity to be reduced. If normal transmission blocks (normal bursts) are used, in contrast to so-called access levels, it is possible to define the reception power by averaging over a relatively large number of bits. As a result, the measurement accuracy rises and a smaller number of repeated measurements is required for transmission power setting. Such relatively long transmission blocks are advantageously used for transmission power setting when timing advance values that are already valid are available.